The invention relates to a birefringent element for use in corrugated waveguide of circular cross section propagating the HE.sub.11 mode, and to a method of manufacturing such a waveguide.
It is frequently desirable in a transmission system to have a birefringent element, either to produce a circular or elliptic polarization, or to eliminate ellipticity introduced by another element, such as a bend in the waveguide. One of the generally accepted desirable properties of the HE.sub.11 mode in a corrugated waveguide is its insensitivity to deformations of cross section as compared to a smooth wall waveguide, (P. J. B. Clarricoats, A. D. Olver, C. G. Parini and G. T. Poulton, in "Proceedings of the Fifth European Microwave Conference," Hamburg, F.R.G., pp. 56-60, September 1975.) For that reason propagation in the HE.sub.11 mode through a circularly symmetric corrugated waveguide is often used. However, generation of a circular or elliptical polarization from a linear polarization has not heretofore been accomplished directly in a corrugated waveguide used for propagation in the HE.sub.11 mode. Instead, any required rotation of the polarization has been achieved before conversion to the HE.sub.11 propagation mode by using a smooth wall waveguide of elliptic cross section propagating the TE.sub.11 or TM.sub.11 mode as a birefringent element, (J. L. Doane, "Int. J. of Electronics," 61, 1109-1133, 1986.) After the change in polarization has been made, conversion to the HE.sub.11 mode may be made for propagation through circularly symmetric corrugated waveguides.